Keying systems for electrical musical instruments for producing steadystate or percussive type tones either separately or concurrently



ly 2 1967 w. MUNCH, JR. ETAL 3,333,041

. KEYING SYSTEMS FOR ELECTRICAL MUSICAL INS'I'RUIVFEII'I'S FOR PRODUCING-STATE OR PERCUSS IVE TYPE TUNES EITHER SEPARATELY OR CONCURRENTLY 2Sheets-Sheet 1 Filed July 9, 1965 3 ELECTRONIC f ELECTRONIC F VALVEEXCITING VALVE f OUTPUT SYSTEM I'IGJ.

EXCITING f 6 CIRCUIT T INVENTORS Fll TE 24 V I WALTER MUNCH,JR 8

ROBERT C. SCHERER ATTORNEYS y 5, 1967 w. MUNCH. JR. ETAL 3,333,041

KEYING SYSTEMS FOR ELECTRICAL MUSICAL INSTRUMENTS FOR PRODUCINGSTEADY-STATE OR PERCUSSIVE' TYPE TUNES EITHER SEPARATELY OR CONCURRENTLYFiled July 5', 1965 2 Sheets-Sheet le r nae 34 I l I W I I I I I I I 2938 I Ic M TON/E j 28 J39 FILTER II FW 4 s PERC I 12 30 37 FILTER- 7 I. I

I' [4c l 35 36 l I I 35 I42 I06 I g i E CHIME .F l T FILTER F ,7 I6 40 ir 4! \OUTPUT sYsTEMl I 32 H I I i lc so 7 I as2 -7g f TONE i l J FILTER8 PERC. 4

OI- FILTER 42 a; 40 CHIME FILTER 4 l OUTPUT SYSTEM INVENTORS WALTERMUNCH,JR. 8 ROBERT C. SCHERER ATTORNEYS United States Patent KEYINGSYSTEMS FOR ELECTRICAL MUSICAL INSTRUMENTS F 0 R PRODUCING STEADY- STATE0R PERCUSSIVE TYPE TUNES EITHER SEPARATELY 0R CQNCURRENTLY Walter Munch,.lr., Park Hills, Ky., and Robert C. Scherer, Cincinnati, Ohio,assignors to D. H. Baldwin Company, Cincinnati, Ohio, a corporation ofOhio Filed July 9, 1965, Ser. No. 470,859 15 Claims. (Cl. 84-111) Thisapplication is a continuation-in-part of our application Ser. No.135,101, filed Aug. 28, 1961, now U.S. No. 3,223,768, and entitled,Keying Systems for Electrical Musical Instruments.

This invention relates to keying systems for electrical musicalinstruments, by means of whichco-ntinuously produced audio signalscorresponding to musical tones can be selected, as desired, fortransmittal to an output system. The term out-put system as used hereinshould be understood, without other qualification, as includingcollecting and tone coloring circuits, amplifying and reproducing means.More specifically, the invention has to do with improved keying circuitsemploying simple, bi-terrninal electronic valves commonly known asdiodes, usually rendered conductive to an audio signal by theapplication of direct current potentials by means of key actuatedmake-break switches.

The diodes used in prior art systems have taken various forms, which maybe classified as (1) vacuum diodes (2) solid-state diodes includingvaristors and (3) gaseous discharge devices, such as type NE-2 neontubes. U.S. Patent 2,483,823, to George falls in the first category,while Rienstra 2,486,208 is in the second group. The third class isinclusive of Faulkner 2,811,069, Anderson et al. 2,811,- 887 andAnderson 2,823,310. Certain inherent disadvantages, from a commercialstandpoint, have been present in various ones of the named systems.These include (1) the necessity for separate bias sources to maintaindiodes non-conductive, (2) the presence of undesired D.C. keyingtransients in output systems during charging of coupling capacitors, (3)presence of signal feed-through in output systems when diodes are notbeing keyed, and (4) the use of many and/ or expensive circuitcomponents.

In view of the above named factors, it is a primary object of thisinvention to provide a keying circuit not requiring a separate biassource to maintain the diode in a non-conductive state.

It is a further object to provide such a circuit which will be free fromundesired D.C. keying transients.

It is an important object to provide a keying circuit having a highsignal-to-feed-through ratio.

It is a still further object to provide a simple, low cost keyingcircuit suitable for use, for example, in electronic organ systemsrequiring several such circuits per playing key.

In U.S. Patent 2,986,984 to Bissonette and Kramer,

I there is disclosed an electronic musical instrument, wherein bothsteady state tone (of the type associated with a pipe organ) andpercussive type tones may be derived separately or simultaneously, thelatter type tones becoming apparent in staccato playing, and the formertype having an efiect only upon the initial, or key down portion of thetone when percussive effects are being achieved. The teachings of thepresent invention may, for example, be employed in instruments of theBissonette-Kramer type, for either or both keying systems. In otherwords, this invention in one facet may be used in the place of variableresistance key switches of the Keck-Jordan type, for example, asdisclosed in their U.S. Patent 2,215,124, to obtain steady state tones.In another facet, percussive elfects may be achieved in the manner, forexample, disclosed in 3,333,041 Patented July 25, 1967 theBissonette-Kramer case or in the U.S. Patent 2,918,- 576 to Munch. Bothlatter patents disclose vacuum triode gate circuits having means tocause gradual decay of the tones. Thus, it is an important object ofthis invention to provide improved, low cost keying circuits suitablefor separate or concurrent use in obtaining steady state and/ orpercussive type tones.

The advent of transistors in generating circuits for electronic organshas lead to low cost frequency dividers of a flip-flop type, whoseoutput is characterized by square waves. This development has madeattractive organ systems of the type disclosed in U.S. Patent 2,571,141to Knoblaugh and Jordan, wherein musical signals of complex, butsymmetrical wave form (characterized by a deficiency or absence of evenorder harmonics), are combined after keying and controlled as toamplitude in such manner as to provide tones having both even order andodd order harmonics. The multiple signal keying required in such asystem for steady state tones can be accomplished by conventional keyingmeans or in accordance with the teachings of this invention. However, ifpercussive type tones having a full complement of harmonics are to bederived from the same symmetrical wave generating circuits as thosesupplying the steady state tones, it is a distinct advantage to be ableto perform the keying function for the percussive tones with a singlemake-break switch. It is therefore an important object of a preferredembodiment of the present invention to provide simple, low cost keyingcircuits capable of producing a'wide range of percussive type voices inan electronic organ employing square wave generators.

It is a further object of the invention to provide improved keyingcircuits for use in electric musical instruments having continuouslyoperating generators of other than square wave.

A primary object of this invention is to provide keying circuits whichnot only obviate the use of variable resistance key switches inproducing conventional type organ tones, with envelopes as desired, but,also will make available so-called sustain characteristics to the tones.

It is a still further object of the invention'to provide a low costkeying system such that chime or carillon type tones may be obtained.

The objects of the invention set forth above, and others which will beset forth hereinafter or will be apparent to one skilled in the art uponreading these specifications, are accomplished in that construction andarrangement of parts of which certain exemplary embodiments will now bedescribed. Reference is made to the accompanying drawings, wherein:

FIGURE 1 illustrates a circuit diagram, partly in block form, of apreferred embodiment of this invention;

FIGURE 2 shows a similar diagram of an alternate form of the invention;

FIGURE 3 is a schematic illustration, partly in block form, showingsomedetail as to an exciting circuit for the diode section of a keyingsystem in accordance with this invention;

FIGURES 3a, 3b and 3c illustrate respectively three different formswhich the diode section of the system of this invention can take;

FIGURE 4 is a schematic illustration of the system of FIGURE 3 expandedto include portions affecting the decay of tones produced by thisinvention:

FIGURE 5 is a schematic diagram showing the application of keyingcircuits to an organ system of the type wherein octavely relatedoscillations are keyed into separate collectors for different footages;

' FIGURE 6 illustrates the application of keying circuits in accordancewith this invention to a system for producing tones simulating chimesand the like;

ice.

FIGURE 7 is a circuit diagram illustrating a modification of the systemof FIGURE 6 adding thereto certain functions available in FIGURE 4.

A preferred basic form of this invention is shown in FIGURE 1, wherein acontinuous signal corresponding to a musical tone is derived from asuitable source 1 via a coupling capacitor 2, for application to abi-terminal electronic valve, such as a diode, designated by the block3. An appropriate output system 4, which may comprise, broadly,collecting and tone coloring means, a conventional amplifier andloudspeaker or other electroacoustic means is shown connected to thediode. To the point is shown connected a block 6 representing anexciting circuit for the diode section 3. The nature of the diode willbe discussed hereinafter, together with the characteristics of theexciting means indicated at 6. As the specification proceeds, it willbecome obvious that the requirements of a particular circuit willdictate whether the exciting circuit merely performs an on-oif functionwith respect to the diode or whether the exciting circuit will producein the output system 4 a tone envelope of a particular shape, such asone with the trailing decay characteristic of a percussive type tone.

An alternate form which this invention, in certain aspects, may take, isillustrated in FIGURE 2, wherein corresponding elements are similarlydesignated. The first of the two circuit loops connected across thesource 1 of FIGURE 2 comprises the diode 3, the capacitor 2 and theoutput system 4, as in FIGURE 1, although the order of the diode andcapacitor is reversed. The second of the circuit loops connected acrossthe source 1 in FIGURE 2 comprises only the diode 3 and exciting circuit6. In both figures the two circuit loops may be closed, as shown, by acommon return path represented by the conventional ground symbol.

As will be explained in greater detail herein-after, the tone signalfrom the continuously operating source 1 of FIGURES 1 and 2 istransmitted to the output system when the diode 3 is changed by theexciting circuit 6 from a state of substantially zero conductivity toone of appreciable conductivity.

Reference is now made to FIGURE 3, the circuit of which is similar tothat of FIGURE 1, except that a simple D.C. exciting path is shown.Corresponding elements of the circuit are similarly designated andconnected. The exciting circuit of FIGURE 3 comprises a DC. source 7connected at one side to a common return 8 and at its other side to asingle-pole, single-throw switch 9, which, in a closed position, canapply the DC. potential to the point 5 via a resistor 10. Although thediode 3 may take several forms, a preferred one in this invention beingone of a solid state type, shown by the appropriate symbol in FIGURE 3b,certain teachings of this invention :may also be applied using diodes ofa gaseous discharge type, indicated in FIGURE 3a at 11, in series with arelatively high resistance 12. It will be obvious that a vacuum diode,indicated at 13 in FIGURE 30, can also be used to practice the teachingsof the invention; although for economic reasons a solid state or gaseousdiode may be preferred. A prime requisite, however, for all diodes usedto practice certain teachings of this invention, is that they becharacterized by one state of substantially zero conductivity andanother state of appreciable conductivity with a positive resistancecharacteristic. Vacuum diodes and solid state diodes currently availablealready meet such a requirement. However, in the circuit configurationsdisclosed herein, a gaseous diode, such as type NE-Z, must have inseries therewith a relatively high resistancesay 5 megohms-sufficient togive a substantial portion of its current versus voltage characteristiccurve a positive slope. Such a keying circuit has already beendisclosed, for use in a system for keying harmonically related signalsthrough a common gate, in a co-pending application, Ser. No. 40,232,filed July 1, 1960 by the same assignee, entitled Gating System forElectrical Musical Instrument,

4 in the name of Alfred J. Bissonette and one of the present inventors,Walter Munch, Jr. (now Patent No. 3,176,060). This assures that thegaseous diode will conduct throughout the audible portion of a gradualdecay characteristic in, for example, percussive type tones, circuitsfor which will be discussed hereinafter.

In the circuit of FIG. 3, the build-up and decay of the tone areaffected by the size of the coupling capacitor 2, that is the larger thecapacitance, the slower the rate at which the tone develops and die-saway. However, the configuration of FIG. 1 may be preferable to that ofFIG. 2, because in the latterthe D.C. charging current to the capacitor2 must flow through the output system 4 and may cause objectionabletransients therein.

Reference is now made to FIG. 4 for the manner in which the decay of thetones can be cont-rolled, although it will be understood that the tonebuild-up may also be affected to some extent in FIG. 4. In FIG. 4,similar portions of the two circuits are similarly designated andconnected, there being an additional resistor 14 in series with theresistor 10 through which the exciting voltage from the source 7 isapplied to the diode 3 at the junction 5. Between the junction point 15and a common return path are connected a decay capacitor 16 and asingle-pole, single-throw switch 17 which may be controlled by a stoptab. Also connected to the junction point 15 is a gaseous diode 18,which, by way of example, may be a commonly known type NE2E, in serieswith a resistor .19, another single-pole, single-throw switch 20 and asecond D.C. source 21.

When it is desired to impose a gradual decay upon a signal keyed by theswitch 9, the switch 17 must be closed prior to keying, thus bringingthe capacitor 16 into the circuit. As the switch 9 is closed, voltagefrom the DC. source 7 charges the capacitor 16 at a rate determined bythe resistor 14 and the capacitor 16. Thus, the buildup of the voltageat the point 5, which determines the rate at which the signal fromsource 1 is gated to the output system 4, is affected by the timeconstant of the capacitor 16 and resistor 14, as well as by the couplingcapacitor 2 mentioned above. The selection of these tone build-upcomponents-Le, resistors 14 and 10, capacitors 16 and 2can be made inaccordance with electrical design principles to achieve the desiredonset to a particular tone.

Upon opening of the switch 9 (assuming switch 17 closed), the charge onthe capacitor 16 is dissipated in the resistor 10, diode 3 and outputsystem 4, at a rate determined by the time constant of the combined elemerits. Should a shortened rate of decay of the tone be desired, it canbe accomplished by the short sustain circuit comprising, for example,the gaseous diode 18, resistor 19, switch 20 and DC. source 21, astaught in a copending application of the same assignee entitled Key- 7ing System for Electrical Musical Instruments, Ser. No. 4,444, filed Jan. 25, 1960, in the name of Walter Munch, Jr.

The voltage of the D0. source 21 is substantially the same as thebreakdown voltage of the diode 18 so that, upon actuation of the switch9 and the firing of the diode 18 (voltages of DC. source 7 and 21 beingadditive), the capacitor will discharge upon opening of switch 9, to alevel where the voltage at point 15 is substantially zero (at whichpoint the diode 3 approaches non-conduction) before the diode 18 ceasesto conduct. It will be obvious to one skilled in the art that theparallel path furnished by the diode 18 circuit will allow the capacitor16 to discharge at a faster rate, resulting in a shorter decay time forthe note keyed into the output system 4.

Although a mere duplication of the circuits of FIGS. 3 or 4 will providesimple systems for playing a plurality of notes for polyphonic music,the system of FIG. 5 illustrates an assembly employing but one switchper key, which will enable a musician to play a 16 foot voice, forexample, simultaneously with an 8 foot voice, as is currentlyaccomplished in commercially available organs using multiple gradualcontact key switches.

Certain keying systems will now be described in connection with FIGS. 5and 6. In these figures the conventional symbol for a solid state diodehas been used; but it will be understood that any of the diodesillustrated or indicated in FIGS. 3a, 3b and 30 may be substituted.

Any of the known solid state diodes which respond to the requirementshereinabove set forth are available for the purposes of this invention.Without limitation, selenium diodes are preferred because they may bemade cheaply. They may also be made in ganged formation as taught inU.S. Patent 3,179,855 to John B. Brombaugh, entitled, Mounting Means fora Diode Assembly, issued Apr. 20, 1965.

Considering in FIG. 5 the key circuit for a source 1 for note Ccomponents corresponding to those of FIG. 4 are similarly designated andconnected. The output of diode 3a is connected to a collector 22, forall 8 signals, to which is connected, as is known in the art, a tonecolor filter 23 of the type, for example, disclosed in the Keck Patent2,233,948. A selector switch 24 preferably actuated by a conventionalstob tab (not shown) serves to direct the modified tone signals to asuitable amplifier and loudspeaker system, designated by the block 25.Other teachings of Kock in the mentioned patent, such as thosepertaining to out-phasing, may obviously be included, if desired.

To the point 15a, corresponding to the junction 15 of FIG. 4, isconnected a resistor a for transmission of DC. from the common source 7to a point b in a keying circuit of similar character, comprisingcoupling capacitor 2aand and diode 3b coupled, as shown to generator 1aof a continuous wave at a frequency corresponding to note C Thus, itwill be seen that a signal an octave below that of the signaltransmitted to the 8 collector 22 will be keyed into a collector 26,which is designated 16 in accordance with standard organ terminology. A16 tone-color filter 27 is shown as modifying the output of thecollector 26 for transmittal to the output system 25 via a stop tabcontrolled switch 28. Thus, with a simple make-and-break switch 9 (FIG.5), a plurality of signals of different -footages can be keyed intodifferent headers, whence they can be modified as to timbre, addedtogether, added in out-of-phase relationship and passed to an outputsystem. Since the onset of the tones can. be controlled by the circuitcomponents as previously discussed, mechanical gradual contact switchesneed not be used; only one switch need be used with each key, and along-life substantially service free system can be achieved.

The keying circuits of this invention can be further utilized to achievechime and carillon effects in an electric musical instrument.

In FIG. 6, a source 10 of continuous tone signals may supply atone-color filter 29 of conventional design via a conventionaldecoupling resistor 30 and resistive key switch 31 for steady stateorgan type tones. If desired, this keying circuit may be of the typepreviously disclosed herein in FIG. 4, for example, or even FIG. 5, iffull exploitation is to be made of the teachings of this invention. Inany event, chime or carillon tones and, if desired, conventionalpercussive effects may be achieved concurrently. While source 10 issupplying conventional organ type tones, with or without sustain of thenature disclosed in FIG. 4, it may also be sending its output viacoupling capacitor to a keying diode 3c of, for example, a solid statetype. Gating voltage for the diode 30 may be furnished from a commonsource 70 via switch 90, resistor 14c and resistor 10c as shown.Similarly, keying voltage may concurrently be supplied to diode 3d and3e via resistors 10d and 10e, respectively, from resistor 140 which hasbeen energized by switch 90 from the source 70. Consequently signalsfrom source 10, previously mentioned, and from harmonically relatedcontinuous wave sources 1d and 1e as coupled into the named keyingcircuits by coupling capacitors 2d and 2e, respectively, concurrentlyappear on collectors 32, 33 and 34 respectively. In accordance withknown musical teachings, appropriate amplitude harmonic components aresynthesized by a suitable resistive summing network 35 into a compositechime or carillon type tone for modification, if desired, by anappropriatefilter 36. Switches 31 and 9c may be operated by a common key314:, the required mechanical coupling between switch 31, switch and key31a being indicated by dotted lines 31b.

If desired further, a conventional percussive tone, such as a vibraharp,may be produced by passage of a signal from one collector 33, forexample, through a suitable filter 37.

Thus, should the performer on an instrument of the type outlined in FIG.6 desire to produce tones of conventional organ character, or of generalpercussive nature, or of chimes, for example, he could, by actuation ofstop switches 38, 39 or 40, respectively, derive the tones from aconventional output system 41, the signals having been collected by abus 42 for the subsequent conversion to sound. The percussive and chimetone would, of course, be achieved by staccato type playing of the keys.Also, in accordance with the teachings of the aforementionedBissonette-Kramer patent, the key-down portion of the tones could bevaried in color by concurrent use of the steady state tone circuit byactuation of stop switch 38. It will be understood in FIG. 6 that theresistive switch 31 and the make-and-break percussive switch 96 arecoupled, i.e., they are actuated by the same playing key. I

Also, it will be understood by those familiar with electric organs thatthere may be other resistive switches similar to 31 connected to otherharmonically generators and to separate headers, such switches alsobeing coupled to the same playing key, so that upon the depression ofsuch key, harmonically related oscillations may be simultaneouslyderived in different headers.

While FIG. 6 shows circuits for the derivation of steady stateoscillations (ordinary organ tones) from generators byresistance-coupled gradual contact switches, it will be evident fromFIG. 5 how capacitatively coupled diode circuits using only a singlemake-and-break switch can be used instead of circuits employing gradualcontact switches. Thus it becomes possible to construct an entire organemploying but two simple make-and-break switches per key, but derivingsimultaneously a plurality of difierent oscillations in differentheaders both inthe steady state system of the instrument and in thepercussive system thereof.

In FIGURE 7 the gating circuit of FIGURE 4 is incorporated into thesystem of FIGURE 6, in order to provide for elimination of the storagecapacitor 16 from circuit by opening switch 17, and for incorporating ashort sustain provision by incorporating diode 18 and its controlcircuitry.

Throughout these specifications numerious omissions of extraneousmaterial have been made in the interests of simplification of thediagrams and descriptions thereof. An example of this lies in the tonecolor circuits of certain figures, wherein only one block has beenshown. It will be understood that a plurality of output systems may beused, as required for example, one for steady state and one forpercussive type tones. Thus many modifications may be made in theinvention without departing from the spirit of it. The invention havingbeen described in certain exemplary embodiments, what is claimed as newand is desired to be secured by Letters Patent is:

1. In an electronic organ,

a plurality of three continuously running tone sources for producingorgan tone,

paths extending from each of said tone sources,

each of said paths including a separate solid state diode gate connectedin cascade with one of said tone sources,

an electro-acoustic load circuit connected in cascade with all saidgates,

means for normally maintaining all said solid state diode gatesnon-conductive,

a source of direct bias voltage,

key switch means including only two switch contacts interposed betweensaid source of direct bias voltage and all said solid state diode gates,

a single operating key for said key switch means, the operating keybeing operable to close said key switch means on depression of said key,

the polarity and amplitude of said direct bias voltage being selected torender all said solid state diode gates conductive to the outputs ofsaid tone sources on actuation of said single key, whereby tone derivedfrom all said tone sources is applied to said electroacoustic loadcircuit on actuation of said single key.

2. The combination according to claim 1 wherein said tone sourcesinclude means which render them harmonically related.

3. The combination according to claim 2, wherein is provided a storagecapacitor connected in charging relation to said source of direct biasvoltage via said key switch means,

' a long time constant discharge circuit means for said storagecapacitor,

one terminal of said storage capacitor being permanently connected toallsaid gates in such relation that its charge tends to maintain said solidstate diode gates all conductive, and said long time constant beingsufficiently long to provide an audible tone sustain on raising of saidkey.

4. The combination according to claim 3 wherein is provided meansincluding a diode device for selectively modifying the discharge time ofsaid storage capacitor, and

means for selectively and at will connecting and disconnecting saiddiode device from said discharge circuit.

5. In an electronic organ,

a plurality of'three continuously running tone sources for producingorgan tone,

paths extending from each of said tone sources,

each of said paths including a solid state diode gate connected incascade with one of said tone sources,

an electroacoustic load circuit connected in cascade with all said solidstate diode gates,

means for normally maintaining all said solid state diode gatesnon-conductive,

a source of direct bias voltage,

means applying said direct bias voltage to all said solid state diodegates simultaneously, the polarity and amplitude of said bias voltagebeing selected to render said solid state diode gates all fullyconductive to the outputs of said tone sources, said tone sources beingharmonically related,

a single storage capacitor connected to corresponding electrodes of eachof said solid state diode gates and in charging relation to said sourceof direct bias voltage,

a long time constant discharge circuit means for said capacitor, saidstorage capacitor being permanently connected to all said gates in suchrelation that its charge tends to maintain said solid state diode gatesall conductive and said long time constant being sutficiently long toprovide an audible tone sustain on cessation of said direct biasvoltage.

6. The combination according to claim 5 wherein is further providedmeans for weighting the relative amplitudes of the tones passed by saidsolid state diode gates sov as to provide a chime tone.

7. The combination according to claim 5 wherein is further providedmeans for selecting one only of the three tones passed by said solidstate diode gates and suppressing the remainder of said tones, said lastmeans comprising a filter connected in cascade with one only of saidgates. 5 8. The combination according to claim 5 wherein is furtherprovided a separate tone collection =bus connected to each of said solidstate diode gates for collecting the tones individually passed by saidsolid state diode gates.

9. The combination according to claim 5 wherein each of said solid statediode gates includes at least one solid state diode in cascade with anofi-biasing capacitor and one of said tone sources, whereby rectifiedcurrents derived from said tone source and stored in said off-biasingcapacitors normally maintain said solid state diodes non-conductive.

10. The combination in accordance with claim 9 wherein said meansapplying said direct bias voltage to all said solid state diode gatessimultaneously includes a separate time constant resistance connectedbetween said single source of direct bias voltage and the junctionpoints of said off-biasing capacitor and said at least one solid statediode of each of said solid state diode gate-s, said time constantresistances being selected to provide a gradual build up of conductivityof said solid state diode gates.

11. In an electronic organ,

a plurality of continuously running tone sources for producing organtone.

paths extending from each of said tone sources,

each of said paths including a separate solid state diode gate connectedin cascade with one of said tone sources,

an electro-acoustic load circuit connected in cascade with all saidgates,

means for normally maintaining all said solid state diode gatesnon-conductive,

a source of direct bias voltage,

a key switch means including only two switch contacts interposed betweensaid source of direct bias voltage and all said solid state diode gates,

a single operating key for said key switch means, the operating keybeing operable to close said key switch means on depression of said key,

the polarity and amplitude of said bias voltage being selected to rendersaid solid state diode gates all conductive to the outputs of said tonesources on closure of said key switch means, whereby tone derived fromall said tone sources is applied to said electroacoustic load circuit onactuation of said single key.

12. The combination according to claim 11 wherein said tone sourcesinclude means which render them harmonically related.

13. The combination according to claim 12 wherein is provided a storagecapacitor connected in chargingrelation to said source of direct biasvoltage via said key switch means,

a long time constant discharge circuit means for said storage capacitor,

one terminal of said storage capacitor being permanently connected toall said gates in such relation that its charge tends to maintain saidsolid state 15. In an electronic organ,

a plurality of continuously running tone sources for producing organtone,

paths extending from each of said tone sources,

each of said paths including a solid state diode gate connected incascade with one of said tone sources,

an electroacoustic load circuit connected in cascade with all saidgates,

means for normally maintaining said solid state diode gates allnon-conductive,

a source of direct bias voltage,

means applying said direct bias voltage to all said solid state diodegates simultaneously, the polarity and amplitude of said direct biasvoltage being selected to render said solid state diode gates allconductive to the outputs of said tone sources, said tone sources beingharmonically related,

a single storage capacitor connected to corresponding 10- electrodes ofeach of said solid state diode gates and in charging relation to saidsource of direct bias voltage,

a long time constant discharge circuit means for said capacitor, saidstorage capacitor being permanently connected to all said gates in suchrelation that its charge tends to maintain said solid state diode gatesall conductive and said long time constant being sufliciently long toprovide an audible tone sustain on cessation of said direct biasvoltage.

References Cited UNITED STATES PATENTS 10/1949 George 84-126 ARTHURGAUSS, Primary Examiner.

J. S. HEYMAN, Assistant Examiner.

1. IN AN ELECTRONIC ORGAN, A PLURALITY OF THREE CONTINUOUSLY RUNNINGTONE SOURCES FOR PRODUCING ORGAN TONE, PATHS EXTENDING FROM EACH OF SAIDTONE SOURCES, EACH OF SAID PATHS INCLUDING A SEPARATE SOLID STATE DIODEGATE CONNECTED IN CASCADE WITH ONE OF SAID TONE SOURCES, ANELECTRO-ACOUSTIC LOAD CIRCUIT CONNECTED IN CASCADE WITH ALL SAID GATES,MEANS FOR NORMALLY MAINTAINING ALL SAID SOLID STATE DIODE GATESNON-CONDUCTIVE, A SOURCE OF DIRECT BIAS VOLTAGE, KEY SWITCH MEANSINCLUDING ONLY TWO SWITCH CONTACTS INTERPOSED BETWEEN SAID SOURCE OFDIRECT BIAS VOLTAGE AND ALL SAID SOLID STATE DIODE GATES,